1,721,057 research outputs found
Comments on the use of expiratory time constant for determinations of plateau pressure, respiratory system compliance, and total resistance
No full text[No abstract available
Nonlinear mechanisms determining expiratory flow limitation in mechanical ventilation: a model-based interpretation
No full textA nonlinear model of breathing mechanics, in which the tracheobronchial airways are considered in three serial segments, is presented to obtain insights into the mechanisms underlying expiratory flow limitation (EFL) in mechanically ventilated patients. Chronic obstructive pulmonary disease (COPD) and normal conditions were simulated and EFL was detected by application of negative expiratory pressure at the mouth or resistance reduction of the expiratory circuit. Simulation results confirm that both techniques reveal remarkable differences in the flow-volume curves between normal subjects and COPD patients, the former showing absence of EFL and the latter exhibiting EFL over most of the expiration. To interpret the role of different nonlinear mechanisms in producing EFL, different flow-volume curves obtained by changing model parameter values were analyzed. An increase in lower-airway resistance did not give rise to EFL, whereas a change in the pressure-volume characteristic of the intermediate-airway segment, towards increased resistance and easier collapse, significantly modified system behavior. In particular, EFL was observed when this intermediate-segment change was combined with an increase in lower-airway resistance. This evidence suggests that modifications, producing loss of radial traction and consequent narrowing of the airways in the peribronchial region, may play a leading role in EFL in COPD patients
Detection of expiratory flow limitation during mechanical ventilation: a simulation study
No full textExpiratory flow limitation (EFL) is frequent in mechanically ventilated patients with obstructive pulmonary diseases and its prompt detection is important to choice the right therapy. Aim of this work is to compare by simulation two methods for detection of flow limitation: the negative expiratory pressure (NEP) method and the external resistance (ΔR) method. To this purpose, a non linear dynamic morphometric model of breathing mechanics, derived from the Weibel symmetrical description of lungs, was used to simulate a normal and an obstructive respiratory condition during artificial ventilation. Both the examined methods reveled the presence of EFL only in the pathological case. The NEP method seems to promote the collapse of the higher and intermediate airways, so producing an overestimation of the pathology. At the contrary, during the ΔR maneuver the same airways increase their radius and, therefore, EFL appears underestimated. The ΔR method seems less practical to use with respect to the NEP method, because of the procedure necessary to choose the right resistance degree, moreover the flow limited portion estimated with the ΔR technique sounds rather dependent to the choice of the external resistance
Impiego di tecniche CADCS per l'analisi e il controllo di dispositivi di assistenza cardiocircolatoria in serie
No full textNearest-neighbor analysis of spatial point patterns: application to biomedical image interpretation
No full textAnalysis of the spatial distributions of objects is fundamental to biomedical image interpretation. Nearest-neighbor (NN) methods are generally used to assess whether objects are arranged at random or in a deterministic manner. Simple standard NN techniques, however, may fail to identify complex spatial organizations. To overcome this problem the present study proposes a NN iterative algorithm that enables deterministic spatial patterns to be detected by identifying the distances between objects for which there is the greatest deviation from randomness and hence the amplitude of the areas of maximum reciprocal influence between objects. The performance of the algorithm is evaluated by applying it to both manufactured and experimental data. The manufactured date example showed that the proposed procedure produced neither false positives or negatives. The method proved to be extremely sensitive, detecting even small deviations from randomness. The experimental analysis was applied to the study of the spatial distribution of apopototic structures in malignant neoplastic tissue. It showed that the apopototic cells and bodies are characterized by a complex spatial pattern, and aggregate closely
A Simulation Study of Expiratory Flow Limitation in Obstructive Patients during Mechanical Ventilation
No full textAlthough normal lungs may be represented satisfactorily by symmetrical architecture, pathological conditions generally require accounting for asymmetrical branching of the bronchial tree, since lung heterogeneity may be significant in respiratory diseases. In the present study, a recently proposed symmetrical dynamic morphometric model of the human lung, based on Weibel’s regular dichotomy, was adapted to simulate different physiopathological scenarios of lung heterogeneity. The asymmetrical architecture was mimicked by modeling different conductive airway compartments below the main bronchi, each compartment being characterized by regular branching. The respiratory zone and chest wall were described by a Voigt body and a constant elastance, respectively. Simulation results allowed us to investigate the influence of the main mechanisms involved in expiratory flow limitation and dynamic hyperinflation in mechanically ventilated COPD patients. In brief, they showed that convective gas acceleration plays a key role in reproducing a negative relationship between driving pressure and expiratory flow. Moreover, reduced lung elastance due to emphysema resulted in a remarkable increase in dynamic hyperinflation, although it did not significantly modify expiratory flow limitation. Finally, the presence of a normal lung compartment masked pathological behaviors, preventing standard techniques from revealing expiratory flow limitation in affected compartments
Real-time tracking of breathing parameters in mechanically ventilated dogs
No full textA recursive identification algorithm with a constant forgetting factor is applied to online identification of the mechanical properties of the respiratory system. The well-known two-parameter model, accounting for pulmonary compliance and resistance, is adopted to characterize breathing mechanics. The algorithm is first tested by using flow and pressure data measured on mechanically ventilated dogs in time-invariant physiopathological conditions. Subsequently, its tracking ability is evaluated on the basis of numerically simulated data in a realistic and well-defined time-varying situation. The results obtained prove that a good tradeoff between tracking ability and noise sensitivity can be reached in the presence of realistic noise levels. The algorithm's computational efficiency allows real-time tracking of the slow parameter changes typical of respiratory pathologies
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